In the past decade, various experiments have been conducted in an attempt to control the collapse distance of plasma filaments generated by an ultra-short pulsed laser (USPL) propagating in air. In some cases, the collapse distance from the laser can be manipulated with the geometry and the setup of focusing optics. It can also be controlled by temporally chirping the laser pulse.
Plasma filaments generated in air via a USPL could be useful in many potential applications. However, the lifetime of these plasma filaments is very short, typically in the nanoseconds range. The short lifetimes are due to recombination of electrons with ions and, more importantly, the attachment of electrons with oxygen molecules forming O2−. For example, a 800 nm USPL delivering femtosecond laser pulses at peak power of 3-10 GW range can create a plasma filament with electron number density as high as 4×1016/cc, initially. At 0.1 nanosecond after the pulse, the recombination process reduces the electron density by an order of magnitude to 4×1015/cc. And at 10 nanoseconds after the pulse, attachment processes reduce electron density further to the 1014/cc level, which is more than two orders of magnitude below the initial density value and too fast for many practical applications. Wherefore it is an object of the present disclosure to overcome the above-mentioned shortcomings and drawbacks associated with the prior art plasma generation having short lifetimes, particularly in air.